Field of the Invention
The present invention relates to a subsurface mining vehicle for collecting mineral deposits from a sea bed at great depths and transporting them to a floating vessel. The invention further relates to a method for collecting mineral deposits from a sea bed at great depths and transporting them to a floating vessel.
Description of Related Art
Deep sea mining involves collecting mineral deposits, such as polymetallic nodules, diamonds, gold, and rare soils from (below) the sea floor 4,000-6,000 m. Polymetallic nodules may for instance comprise nickel, copper, cobalt and manganese nodules. In deep sea mining, the sea floor may be a distance of up to 5000 m and more away from the sea surface, and developing equipment for deep sea mining imposes many challenges.
Deep sea mining vessels need to bring subsurface mining equipment to the sea floor and recover the same from the sea floor after termination of a mining operation. Typical vessels thereto comprise some type of launching and docking device that is operated from a docking well. Such docking well passes through and is enclosed by the vessel hull, and opens to the sea at its bottom side defining a so-called splash zone of the docking well. The docking well may be closable across the bottom by movable gates if desired. A deep sea mining vessel further typically comprises pumping equipment for bringing mined mineral deposits from the sea floor to a vessel storage hold through a transport pipe system. A riser string extends from the vessel to the mining equipment to convey the mined mineral nodules towards the sea surface. A lift system is usually operational in raising and launching the riser string.
U.S. Pat. No. 4,232,903 discloses a subsurface mining vehicle for collecting mineral deposits from a sea bed and transport said deposits to a floating vessel. The mining vehicle comprises a load-bearing structure provided with propelling means for advancing the vehicle on the sea bed. The vehicle is equipped with a pick-up unit and with a frame that is used to attach the vehicle to a towing cable. During deployment of the vehicle, the frame remains in a vertical position in line with the cables from which it is suspended. When the vehicle is resting on the sea floor, the frame is dropped over to a more horizontal drag or tow position.
WO 2012/134275 A2 discloses a mining or dredging vehicle. The vehicle can be suspended from cables and a riser to mine or dredge materials from a sea bottom. The vehicle comprises a sledge construction with a support surface, the orientation of which is adjustable by hydraulic cylinders relative to a frame of the vehicle. A suction height controller is provided to control the height of an excavating head and thereby switch between a ‘sledge mode’ and a ‘gliding mode’. The vehicle is further provided with an adjustable suspension arranged to mechanically connect to a towing cable. The adjustable suspension allows controlling the angle under which the towing cable exerts a towing force on the vehicle during movement along the sea bed and to achieve a better trim control.
WO 2012/158028 A1 discloses a generally known suction dredging vessel, provided with a suction pipe, to which suction pipe is attached a remotely controlled mining or dredging vehicle. The connection is through a flexible riser.
In launching subsurface mining equipment, the maximum environmental circumstances are often limited to certain wave heights, and considerable time is lost while waiting for a weather window for deploying or recovering the equipment. Further, most damages to subsea mining equipment occur during launching and recovery. Given the size, complexity and cost of a mining vehicle, this is unacceptable.
The above described disadvantages occur to an even higher extent in launching and recovering subsurface mining equipment. Indeed, deep sea mining equipment preferably has a relatively low weight, which makes it difficult to control such equipment when suddenly contacting a moving mass of water. The risk for collision with parts of the vessel or other structures is high.
Therefore, an aim of the present invention is to provide a device and method for launching subsurface mining equipment into a water mass from a docking well of a floating vessel, and recover said equipment from the water mass in a more controlled manner.